1. Field of the Invention
The present invention relates to an ink tank which is constituted to be attachable/detachable with respect to a recording head mounted on an ink jet recording apparatus, generally to an ink tank in which an ink tank size of a direction substantially vertical to an abutment direction is small with respect to an ink tank size of the abutment direction onto an ink supply tube of an ink jet head, and in which a so-called aspect ratio is high with respect to the abutment direction onto the ink jet head, particularly to an inventive and improved ink tank in which the constitution of an ink absorbing material contained in the ink tank is defined, a defect is inhibited from being generated in an internal structure by an external factor, and a stable ink supply capability can be fulfilled.
2. Description of the Related Art
In a field of ink jet recording, in a constitution in which an ink jet head is united with an ink tank from viewpoints of miniaturization of an apparatus and a maintenance-free apparatus, it is known that an ink jet cartridge set to be attachable/detachable with respect to a mounting portion (scanning carriage) of an ink jet recording apparatus is used. In the ink jet cartridge, for example, a constitution in which the ink jet head is constantly united with the ink tank, and a constitution in which the ink jet head and ink tank are attachable/detachable and united during the use are known to be used.
The ink tank for use in the ink cartridge is required to steadily hold an ink so that the ink does not leak to the outside in an unused state for recording, and to steadily supply the ink to the ink jet head during the recording. To satisfy this requirement, the ink tank includes a constitution for generating a back pressure against a flow of ink supplied to the ink jet head, that is, a so-called negative pressure.
Examples of a general constitution for generating the negative pressure in the ink tank include an constitution described in Japanese Patent Application Laid-Open Nos. 62-264728 and 8-230207 in which a porous material such as urethane foam is contained as a negative pressure generating member (ink absorbing material) in the ink tank, and a capillary force of the porous material is used as a negative pressure generation source. The ink tank for use in the constitution usually includes: an ink container in which an ink absorbing material for storing the ink is contained; an ink supply port for supplying the ink to the ink jet head from the ink absorbing material; and an atmosphere communicating port for taking atmospheric air into the ink container in order to smoothen ink supply during the recording.
Moreover, in order to steadily supply the ink to the ink jet head, the ink absorbing material is contained inside the ink tank in such a manner that an ink holding force in the ink supply port of the ink tank and a periphery of the port is high as compared with other regions. Furthermore, a condition is generally constituted such that the ink easily gathers in the vicinity of the ink supply port.
Examples of a method for raising the capillary force include a method, described in the Japanese Patent Application Laid-Open No. 8-230207, comprising: containing ink holding members (ink absorbing materials) including a first ink holding member 250 for collecting the ink in the vicinity of the ink supply port to an ink jet head 232 and a second ink holding member 251 for holding the ink in a housing 211 of an ink tank 210 as shown in FIG. 7A; setting the ink holding force (capillary force) of the first ink holding member 250 to be not less than the capillary force of the second ink holding member 251; and allowing the first ink holding member 250 to constantly hold the ink so that the ink is steadily supplied. This system is generally known. For example, a constitution is known in which an urethane ink absorbing material is used in the second ink holding member 251 and the ink holding member formed of a fiber bundle is used in the first ink holding member 250.
The first ink holding member 250 is constituted of the bundle of fibers arranged along an ink supply direction. As shown in FIG. 7B, when the ink tank 210 is mounted onto the ink jet head 232, in order to allow an ink receiving tube 234B on an ink jet head 232 side to firmly abut on the first ink holding member 250, the first ink holding member 250 slides towards the second ink holding member 251, and pushes inwards the second ink holding member 251 so as to compress the second ink holding member in this mode.
In the above-described mode, the first ink holding member 250 formed of the fiber bundle is constituted by compressing the fibers with a high pressure, and is therefore hard and is not easily deformed as compared with the second ink holding member 251 formed of urethane. Therefore, when the ink receiving tube 234B is inserted via the supply port of the ink tank, the first ink holding member 250 slides, this sliding is absorbed by the deformation of the second ink holding member 251, and a restoring force of the second ink holding member 251 is used to achieve stable abutment among the ink receiving tube 234B, first ink holding member 250, and second ink holding member 251.
Additionally, since the ink tank is contained/held in the ink jet recording apparatus, an outer shape of the ink tank is sometimes determined as a requirement on the ink jet recording apparatus side. Therefore, there has been a demand for not only an ink tank in which an aspect ratio is balanced but also an ink tank which is longer than is wide, a thin ink tank, and the like.
The ink tank is attached/detached with respect to the ink jet head. Therefore, for example, an operator drops the ink tank in handling the ink tank, or another rapid external impact is sometimes applied to the ink tank.
When a large external impact is added, the second ink holding member 251 occupying a large volume in the ink tank sometimes moves and is deformed in the ink tank. The slightly deformed ink holding member can be restored by elasticity thereof, but the member is not restored depending on a degree of deformation. The ink holding force rises in a deformed portion, the ink remains in the corresponding portion, and a drop of ink consumption efficiency might be caused. Moreover, there is also a possibility that ink leak is caused.
Particularly, in recent years, an amount of ink held in the ink tank so that the tank is impregnated with the ink has tended to increase with a rise of a recording frequency by the ink jet recording apparatus. When the ink amount held in the ink holding member increases more in this manner, the impact applied to the ink holding member during the falling increases. This results in an environment in which the above-described disadvantage is easily generated.
For a problem of deformation generated in the second ink holding member contained in the ink tank by the external factor, among ink tanks having various outer shapes, particularly in an ink tank in which an ink tank size of a direction substantially vertical to an abutment direction onto an ink supply tube of the ink jet head is small with respect to an ink tank size of the abutment direction, and in which a so-called aspect ratio is high with respect to the abutment direction onto the ink jet head, the second ink holding member tends to be easily deformed by the impact as compared with ink tanks having other constitutions.
Additionally, in recent years, an ink tank has been proposed in which a thermoplastic resin is used in the second ink holding member instead of urethane from viewpoints of ecology and recycling efficiency. A rebound resilience is small in the ink holding member formed of a resin material as compared with urethane. Therefore, when the ink holding member holding a large amount of ink moves or buckles by the impact during the falling, the shape of the member is not easily restored. Also in this case, in the ink tank whose aspect ratio to the abutment direction onto the ink jet head is high, the second ink holding member similarly tends to be easily deformed as compared with the ink tanks having other constitutions.